US EPA

1632958 

Journal Article 

Design and Control of Heterogeneous Azeotropic Column System for the Separation of Pyridine and Water 

Wu, YiC; Chien, IL 

2009 

Yes 

Industrial and Engineering Chemistry Research
ISSN: 0888-5885
EISSN: 1520-5045 

48 

23 

10564-10576 

10.1021/ie901231s 

WOS:000272039200051 

The design and control of two types of separation systems
using heterogeneous azeotropic distillation have been studied in the literature. One type (e.g.,
isopropyl alcohol dehydration) is to add a light entrainer (cyclohexane) into the system so that
a minimum-boiling ternary azeotrope is formed which can split into two liquid phases in a
decanter. This type of system also introduces two additional azeotropes (isopropyl alcohol-
cyclohexane and water-cyclohexane), thus dividing the ternary system into three distillation
regions. Another type (e.g., acetic acid dehydration) does not contain azeotrope in the original
system. However, due to a tangent pinch near the pure water end ail entrainer (isobutyl acetate)
is added into the system to aid the separation. This type of system has only one binary
heterogeneous azeotrope (water-isobutyl acetate); thus there is only one distillation region. In
this paper, design and control of a different residue curve map (RCM) type of separation system
utilizing heterogeneous azeotropic distillation will be studied. An example of this RCM type is
pyridine and water separation using toluene as entrainer. Adding toluene into this system
introduces two additional azeotropes, one is minimum-boiling binary heterogeneous azeotrope
(water-toluene) and the other one is a binary homogeneous azeotrope (pyridine-toluene). There is
no ternary azeotrope for this system. Two alternative design flow sheets are compared in this
paper to find the one which is most economical and also meet stringent product purity
specifications. A simple overall control strategy of this process has also been developed which
requires only one temperature control loop in each column.